1. Field of the Invention
This invention relates to fiber optics and, in particular, to an interconnection for connecting a fiber optic cable to fiber optic circuitry running parallel to the surface of circuit boards and other equipment.
2. Description of the Prior Art
The recent development and adaptation of fiber optic technology to communications, data processing, and similar transmission systems result in numerous advantages as compared with electrical and electronic systems which have comparable functional objectives. Low-loss, high quality, multimode fiber optic cable has been developed which makes practical optical systems both feasible and desirable. Some of the advantages of fiber optic cables used in such systems include greatly reduced size, weight, and cost; electrical isolation which eliminates grounding and ground loops; and, easy coupling to common logic circuitry by use of available light sources and detectors. Moreover, fiber optic cables permit high channel isolation, easy interchangeability with electrical cable, and greatly reduced electromagnetic interference.
In military use, one of the most important advantages offered by fiber optic cables is their characteristic immunity to radio frequency signals and the fact that the transmitted light signals are contained wholly within the cable. This obviously greatly increases transmission security, particularly for ground communications systems. The use of optical cables also eliminates cross talk and inductive coupling, and the optical paths provided by fiber optic cables are resistant to electromagnetic interference from other equipment. In addition, fiber optic systems are immune even to electromagnetic pulses, such as may be generated by nuclear explosions. A further important advantage of fiber optic systems is their inherently higher data rate capability.
When optical cable systems are used in aircraft, particularly of the smaller military types, they are exposed to and are required to operate in harsh environments, they have limited space for routing during installation, and they are subjected to considerable handling during their service life. Because fiber optic cable harnesses in general use do not differ visually from their electrical counterparts and will, therefore, receive the same rough treatment, the components of fiber optic cable systems, particularly the interconnections used therewith, must be as durable as electrical interconnects. There is a need, therefore, for a fiber optic cable interconnection that is as durable as an electrical connector and which is suitable for indiscriminate mixing with electrical interconnect systems. In additions, because of space limitations in electro-optical equipment that are now coming into use, there is a need also for fiber optic interconnections which can be connected into circuit components having fiber optic circuitry disposed normal to the axis of the connection itself.
Because of the requirement for precise alignment and to avoid damage to the connections, it has been a practice in the prior art to provide fiber optic terminations that are embedded or otherwise fixed on the circuit board or component to which the fiber optic is connected. Examples of such techniques are shown in the prior art by R. W. Lindsey, U.S. Pat. No. 3,777,154; J. P. Palmer, U.S. Pat. No. 3,963,920; and N. J. Hansen et al., U.S. Pat. No. 4,170,399.
A teaching of a plug-in connector for a fiber optic signal conduit combined with an electrical power conduit is disclosed in the prior art by R. A. Meade, U.S. Pat. No. 4,081,208. In Meade, however, instead of an interconnection for a circuit board having the circuitry embedded parallel to the surface as is the case in the present invention, an on-axis connection to an optical circuit component is taught. Disclosed in Meade is the straightin interfacing of the end of an optical signal conduit which plugs into a receptacle mounted on the face of the circuit board, the optic signal receiving apparatus being a part of the receptacle itself. There is no teaching in the prior art, therefore, of an optical fiber cable connector that plugs into a circuit board receptacle, the connector being furnished with means providing a signal path to an optical fiber that is routed parallel to the surface of the board.